By combining microdrop in situ hybridization and flow cytometry, Phase I studies demonstrated that specific RNA sequences present in high or lower copy numbers (which comprise only 2-4% of the total RNA), including HIV-l RNA, can be detected. The assay's high sensitivity makes it a powerful diagnostic tool. In Phase II research, the assay format will be adapted to detect sub-populations of cells infected with retroviruses for both research and clinical applications. Using clinical samples, human blood cells infected with HIV-l will be identified. Using a model human cell line, assays will also be developed to identify cells infected with HIV-2, HTLV- I, and HTLV-II. Current blood based clinical assays which detect the presence of retroviruses and human T-cell lymphotrophic viruses are not optimal. Conventional fluorescence in situ hybridization methods require fixation, which reduces cell recovery as much as 50% and makes detection of small sub-populations of infected cells difficult. Conventional assays are also plagued by low hybridization efficiency and poor reproducibility. The gel microdrop (GMD) assay overcomes current limitations, including improving cell recovery to at least 90%. PROPOSED COMMERCIAL APPLICATION: By permitting rapid detection of the presence of small amounts of virus- specific nucleic acids, the proposed assay will significantly impact disease diagnosis, monitoring, and treatment, as well as blood screening.